1. Field of the Invention
This invention relates to the field of biosensing and, more particularly, to an improved method and system for analyte sensing mediated by adapter/carrier molecules which act as an adapter between the analyte and sensor element or deliver the analyte to the sensor element.
2. Description of the Background
Stochastic sensing is based on the detection of individual binding events between analyte molecules and a single receptor, which acts as a biosensor element. The read-out depends on a property of the receptor, usually a protein, that is altered when the binding site is occupied. In its simplest manifestation, stochastic sensing provides a binary signal (occupied/unoccupied) comprising fluctuations in, e.g. electrical current, fluorescence, or force. The frequency of occurrence of the binding events is determined by the concentration of the analyte. The nature of the binding events, e.g. the magnitude and duration of the associated signal, is determined by the properties of the analyte. The ability to identify an analyte by its characteristic signature is a distinctive feature of stochastic sensing.
The ability to observe changes in the state of single protein molecules has been available with respect to ion channels for over twenty years. The electrical currents generated by the large ion fluxes through these molecules (e.g., 108 s−1) can be monitored by single channel recording. More recently, structural changes in single protein molecules have been detected by fluorescence techniques and by force measurements (Doleman, B. J., et al., Proc. Natl. Acad. Sci. USA 95:5442-5447, 1998; Hellinga, H. W., et al., Trends Biotechnol. 16:183-189, 1998; Czarnik, A. W., Nature 394:417-418, 1998).
Genetically engineered versions of the bacterial pore forming protein α-Hemolysin (αHL) have been used as sensor elements. Current stochastic schemes are limited in that the type of analytes that can be sensed are restricted to those which interact with the pore. Current schemes cannot be used, for example, to analyze organic molecules, molecules insoluble in aqueous media and certain mixtures of analytes.
Better sensors would be useful in many situations. For example, in medicine, improved means for detecting physiological markers and therapeutic agents are needed; in environmental protection, various pollutants and effluents from factories must be monitored more thoroughly; for defense, new ways to detect explosives and chemical and biological agents are urgently required. In only a few cases are the available technologies optimal for the task at hand. Better devices are needed with improved sensitivity and rapid “real time” response.
There is therefore a need for analyte sensors, including stochastic biosensors, that can detect the presence and concentration of a wider variety of analytes as well as samples containing mixtures of analytes.